Third, the effectiveness of hybrid dense–sparse fusion appears to be understated in the original DPR paper.
[1]} found that hybrid retrieval is less effective than dense retrieval in most settings, which is inconsistent with our experimental results.
Instead, we found that dense–sparse retrieval consistently beats sparse retrieval across all settings.
The gains from both hybrid scoring techniques are statistically significant, with the exception of top-20 for CuratedTREC.
Our results might be due to better BM25 effectiveness, but we are unable to further diagnose these differences because, once again, the hybrid retrieval code is not provided in the DPR repo.
Further testing also found that the differences between the two hybrid techniques are not significant.
Thus, there does not appear to be a strong basis to prefer one hybrid technique over the other.
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